Time Series Analysis - Please help!

System
System Posts: 100,534 🤖 Admin 🤖
edited June 18 in AAT student discussion
I am confused when using time series analysis to forecast future sales.<BR>I have a bizarre calculation in one of my notes from ages ago which reads as y=400+20x.<BR>I understand all of it until my working is written as - 400+(20x21) x0.95.<BR>The 0.95 is based on a -5% Seasonal variation so I understand that. Can you tell me where I would have got the 21 from ?????? This was for a forecast of sales for Q1, I also have the other quarters forecasts using 22, 23 and 24. Is this related ?<BR>Please advise as I would like to move on from this subject !!!<BR>Also in this area, I have read an article by Andrew Harrington on the Accounting Technician mag website which clearly explains all of the forecasting sales using Time series (except the bit I am stuck on), but I do not understand where he gets the Trend Figures for 2002 from after he has completed the moving averages. He then add/subtracts the seasonal variations to get the forecasted sales figures. But where do the <BR>3,394, 3,460, 3,527, 3,593 come from ???? <BR> <BR>Thanks very much indeed !! In desperate need of assistance !!<BR> <BR>

Comments

  • System
    System Posts: 100,534 🤖 Admin 🤖
    Time Series Analysis - Please help!

    The "21" means that this is the 21st quarter you are forecasting for. The formula is constructed using regression analysis on the previous 20 quarters (or something like that)<BR><BR>It may be good for you to get a copy of the June 2003 PAR Paper which had a very similar question in section 2. Also if you query "PAR" on the general forum this will give you all the discussions relating to this question after we had sat this exam.<BR><BR>Hope this kind of helps
  • System
    System Posts: 100,534 🤖 Admin 🤖
    Time Series Analysis - Please help!

    Thanks for your help, I actually worked out the second part of my question myself by accident !! Thanks for your advice on the first bit though. How can I get hold of a past paper ??? cheers
  • System
    System Posts: 100,534 🤖 Admin 🤖
    Time Series Analysis - Please help!

    Hi Ninki,<BR><BR>There is already a reply to the linear regression bit of your post, so I'll reply to the bit about my article!<BR><BR>The trend figures for the forecast are based on a simplistic attempt to extend the trend of moving averages.<BR><BR>If you look at the centred trend, it increases from £2,463 to £3,194 in 11 quarterly "jumps" - this represents an average increase of £66.5 or so per quarter. The last trend point corresponds to quarter 2 of 2001, so to extend to quarter 1 of 2002 I have added on 3 lots of £66.5. To go further, each quarter is increased by another £66.5.<BR><BR>The assumption is that since the centred trend is (almost) a straight line, it will continue in this fashion.<BR><BR>Hope that helps. I didn't put it in the article because I wanted to concentrate on the seasonal variations.<BR><BR>Good luck!<BR><BR>Andrew Harrington
  • System
    System Posts: 100,534 🤖 Admin 🤖
    PAR Exam paper June 2003

    Can anybody help me with above paper and answer sheet?<BR>My E-mail is vdwaltmj@eskom.co.za

Categories

Privacy Policy